Sudan grass management for control of cyanide poisoning

The purpose of this investigation was to determine the factors involved in cyanide poisoning of livestock by Sudan grass in order that a program of crop management might be formulated which would eliminate this danger. In the course Of this investigation, a rapid chemical method for determining the cyanide content of Sudan grass and sorghum was developed. This method has proved invaluable in elucidating the factors involved and in determining whether or not Sudan grass is safe to pasture. The results obtained are summarized as follows: It is the short, dark green Sudan grass which is high in cyanide and which is dangerous to pasture. Second growth, after pasturing or removal of a hay crop, when short and clark green is especially dangerous. Sudan grass which is 2 feet or more in height, whether first or second growth, is low in cyanide and is relatively safe to pasture. Sudan grass, short or tall, which is of a pale or yellowish green color is low in cyanide and is relatively safe to pasture. Both from the standpoint of danger from poisoning and possibility of obtaining the most pasture, Sudan grass should usually not be pastured until it has reached a height of 18 inches and better, 2 or 3 feet. This is best accomplished by having two or more fields so that the cattle may be rotated from one field to another. A high level of available nitrogen and a low level of available phosphorus in the soil tend to increase the poison content, while a low level of available nitrogen and a high level of available phosphorus have the opposite effect. A high cyanide content may still occur in short plants, however, especially in the second growth, even though the level of available phosphorus is high. A high level of available phosphorus along with other favorable growth factors makes it possible for the plant to attain quickly a height of 2 to 3 feet, at which stage it is relatively free of poison. Drought probably operates as a factor, largely by keeping the plants small when they are always much higher in cyanide than when larger. Drought keeps the plants small by withholding water and probably lessening the availability of phosphates to plants much more than that of nitrogen. Fall or early spring plowing followed by cultivation should be practiced on fields to be sown to Sudan grass so as to conserve moisture and prevent the ill effects of drought. When Sudan grass is dried and made into hay without undue exposure and then well stored, the cyanide content does not change greatly. Since it is usually not cut for hay until it reaches a height of 3 feet or more, there is little if any danger of cyanide poisoning from Sudan grass hay. However, if short Sudan grass, high in cyanide, is made into hay, it will be dangerous as a feed. Cattle when turned into Sudan grass of high poison content usually stop eating after about 15 minutes due to the action of the poison. If the animals are not too hungry and are in a high state of vigor, they may stop eating before they take a fatal dose. Cattle vary in the amount of cyanide that it takes to be fatal. If they are in a low state of vigor and very hungry, they are more apt to eat a fatal dose than when the opposite is the case. When there is doubt as to possible danger, samples should be collected and tested for poison. The whole field should be examined carefully. If spots of small Sudan grass are found, samples from each of these should be taken for analysis.